In a wireless communication apparatus, to achieve normal communication, the power of alternating current (AC) signals, such as modulated signals and demodulated signals, that are input and output within the apparatus is detected, and control is performed in accordance with detection results. To detect the power of an AC signal, for example, a detector circuit is used. FIG. 10A illustrates an example of a configuration of an existing detector circuit that uses a diode as a rectifier element. The detector circuit illustrated in FIG. 10A includes capacitors 1001 and 1005, an inductor 1002, a diode 1003, a resistor 1004, and a direct-current (DC) voltage source 1006.
One electrode of the capacitor 1001 is coupled to a transmission path for transmitting an AC signal to be detected, and the other electrode is coupled to the anode of the diode 1003. One end of the inductor 1002 is coupled to the anode of the diode 1003, and the other end is coupled to the DC voltage source 1006. The cathode of the diode 1003 is coupled to a node that outputs an output voltage VOUT. One end of the resistor 1004 is coupled to the cathode of the diode 1003, and the other end is coupled to a reference potential (for example, the ground). One electrode of the capacitor 1005 is coupled to the cathode of the diode 1003, and the other electrode is coupled to the reference potential.
An AC signal biased by a bias voltage generated by the capacitor 1001, the inductor 1002, and the DC voltage source 1006 is input to the anode of the diode 1003. The diode 1003 rectifies the AC signal input to its anode to output a signal (voltage) in accordance with the power of the input AC signal. The high-frequency component of the signal (voltage) output from the cathode of the diode 1003 is removed by a low-pass filter including the capacitor 1005 and the resistor 1004, and the resultant signal is output as an output voltage VOUT. In such a way, the detector circuit illustrated in FIG. 10A outputs a DC voltage signal as the output voltage VOUT in accordance with the power of an input AC signal.
The detector circuit illustrated in FIG. 10A exhibits temperature characteristics as illustrated in FIG. 10B due to the temperature characteristics of the diode 1003. FIG. 10B is a diagram illustrating temperature characteristics of the detector circuit illustrated in FIG. 10A, and the horizontal axis represents power Pin of an AC signal that is input and the vertical axis represents the output voltage VOUT. FIG. 10B illustrates characteristics 1011 at a temperature T11, characteristics 1012 at a temperature T12, characteristics 1013 at a temperature T13, characteristics 1014 at a temperature T14, and characteristics 1015 at a temperature T15. The temperatures T11 to T15 are such that T11 (low temperature)<T12<T13<T14<T15 (high temperature).
As illustrated in FIG. 10B, when AC signals with the same power Pin are input, the output voltages VOUT of the detector circuit differ depending on temperature, such that the higher the temperature, the higher the output voltage VOUT. In a detector circuit using a diode in such a manner, the output voltage VOUT varies with temperature change. The temperature of the wireless communication apparatus varies and is not fixed because of heat generation inside the housing or environmental temperature, and therefore it is difficult to accurately detect the power of an AC signal.
The followings are reference documents.
[Document 1] Japanese Laid-open Patent Publication No. 2005-151331 and
[Document 2] Japanese Laid-open Patent Publication No. 2008-148214.